A hot runner injection molding apparatus typically includes nozzles that are heated to maintain melt therein at a controlled temperature. The nozzles are typically in contact with a mold component that defines one or more mold cavities. The mold cavities in the mold component are filled with melt that first passes through the nozzles. The mold component is then typically cooled in order to solidify the melt in the mold cavities, thus forming a plurality of molded parts, which are then ejected from the mold cavities.
Because the nozzles are typically heated, and the mold component is cooled for at least a portion of an injection molding cycle, it is desirable to have a relatively low heat transfer from the nozzles into the mold component. Many nozzle constructions have been proposed in the past to address this issue.
An example of such a nozzle construction is shown in U.S. Pat. No. 5,554,395, to Hume et al. The '395 patent teaches a multi-piece nozzle tip assembly including a tip piece, a tip surrounding piece and a resilient element. The resilient element is provided between the tip piece and the mold component, to inhibit melt leakage therepast. However, heat can be lost from the tip piece through the resilient element and into the mold component. In particular, the heat losses occur near the downstream end of the tip piece, where control over the temperature of the melt is particularly important.
Thus, there is a continuing need for new nozzle constructions that have further improved heat transfer efficiency.